The present invention relates to a precision slit of adjustable width, wherein the slit is defined by and between slit jaws which are connected for adjustment of slit width via a system of parallelogram linkages.
Illustratively, such precision slits are used as entrance or exit slits in monochromators, spectrophotometers or other spectral instruments which operate in the infrared, visible or ultraviolet range, or in the range of X-radiation. In this connection, it is important to be able to adjust the slits very accurately and in reproducible manner. The adjustment mechanism for the slit jaws must also operate substantially without play and must assure exact parallelism of the slit-defining edges of the slit jaws in every position of adjustment.
U.S. Pat. No. 2,587,451 discloses a slit for spectroscopic instruments in which the slit jaws are arranged on levers which are mounted for guided displacement. In order to adjust slit width, an element is provided which acts via loading springs both against these levers and against an adjustment member. With this solution, precision is limited by the guides of the slit-jaw levers and by friction in the guides.
East German Patent 42,809 discloses a slit for a spectrophotometer in which displacement mechanism for the slit jaws operates without guides. In that solution, each slit jaw is guided by its own parallelogram linkage and is connected to one side of its parallelogram. The displacement mechanism is developed as a lever system which acts on the parallelogram for one of the slit jaws, and this lever system is connected in force-locked manner via another lever system to the parallelogram of the other slit jaw. Since friction occurs at the point of contact of the two lever systems, absolute reproducibility of the adjustment is not possible. Furthermore, such guidance of the slit jaws cannot assure that the slit-limiting edges will be exactly parallel to each other, in every adjusted position.